One popular type of home is what is considered in the construction industry a timber frame home. Timber frame homes are constructed of a plurality of heavy timber frame members and are designed so as to expose the timbers of the frame inside the home.
Traditionally a conventional light frame was built around or between the timber frame members, a layer of drywall secured to the inside surfaces of the light frame members, fiberglass insulation inserted between the light frame members, and then covered on the outside with siding. However, this method of construction was slow, labor intensive and costly. In addition, the resulting building or structure was not energy efficient because the insulation was interrupted every 16 inches by a light frame member (stud) or rafter allowing heat to easily escape and cold to enter the building at these points.
In the 1970's, structural insulating panels, commonly known in the industry as stress-skin panels, were developed for use in the residential construction of timber frame homes. The stress-skin panels are nailed to the exterior of the timber frame members leaving the frame exposed inside the home, thus creating an attractive appearance. These stress-skin panels used in conjunction with a timber frame replaced in many applications the standard 2.times.4 construction of homes. The stress-skin panels were considered stronger than 2.times.4s and were considered to provide better insulating capability.
A stress-skin panel is a panel comprising an outer skin, an inner skin and several inches of rigid foam insulation sandwiched between the two layers of sturdy sheathing material or skins. The outer and inner skins may be constructed of a plurality of materials, but are usually made of plywood, waferboard or oriented strand board (OSB). The foam insulation core located between the two skins is expanded polystyrene (commonly called EPS) or urethane foam, typically 3 1/2" thick. These panels are typically prefabricated before being installed as part of the walls and roofs of structures like homes, commercial offices, etc.
Because both plywood and OSB are commercially available only in certain size sheets, the size of the stress skin panels is limited. For example, plywood is typically available in 4'.times.8' sheets while OSB is typically available in larger size sheets (up to 8'.times.24'). Therefore, the size of the stress-skin panels is limited to between 4'.times.8' and 8'.times.24'. Due to the limited size of the stress-skin panels, a large number of panels must be used in order to completely construct a roof or the perimeter walls of a building. Additionally, due to the weight of the stress-skin panels, a crane is often required to lift the stress-skin panels into place, particularly when the stress-skin panels are used to construct a roof. The relatively large number of stress-skin panels necessary to construct such a roof requires a large number of individual laborers and additionally requires a large amount of crane time (time that the crane is in use). Both of these requirements increase the cost of constructing a timber frame building using stress skin panels.
Stress-skin panels are manufactured by injecting a liquid urethane between the two skins and allowing the liquid urethane to expand between the skins, the urethane foam adhering to the inner surfaces of the skins without any other adhesives. Alternatively, if the foam insulation is EPS, the foam insulation is glued or adhesively secured to the outer sheathing layers or skins with a urethane glue. With either type of insulation, over time the adhesive or bond used to secure the foam insulation to the two skins of the panel may deteriorate if exposed to extreme temperature fluctuations causing the inner and outer skins of the panel to sheer apart from the foam insulation.
In addition, some type of sealant must be inserted along the joints between adjacent stress-skin panels in order to reduce air and moisture flow through these joints. Alternatively, thin horizontal splines may be used between panels to minimize thermal breaks. Improperly sealed joints or seams can allow moisture to collect and the trapped moisture can eventually cause the materials of the stress-skin panels to swell and deteriorate.
These stress-skin panels are secured to the heavy timber frame of a structure with long nails or screws known in the industry as pole, barn spikes or deck screws. The length of these nails or screws must be greater than the depth of the stress-skin panels so that the panels may be secured to the exterior surfaces of the timber frame members of the structure, the nails or screws passing through the entire stress-skin panel and into the timber frame members.
In cold climates where a large temperature differential exists between the exterior surface of panels and the interior of the structure, the nails or screws running through the panels may conduct heat and may cause condensation at the heads of the nails or screws. Over time, this condensation may cause the exterior layer of the stress-skin panels to rot which may eventually cause structural failure of the panels.
In addition, utilizing stress-skin panels to construct a timber frame home is expensive. Because the interior layers or skins of the stress-skin panels are visible from inside the building, another layer of material such as drywall or wood paneling is typically placed over and attached to the inner layer or skin of the stress-skin panels in order to make the inner surfaces of the panels aesthetically pleasing. Similarly, a layer of siding or other material is usually placed over the outer skins of the stress-skin panels.
If conventional stress-skin panels are used to construct the roof of a building, asphalt-saturated felt (known in the industry as tar paper) is applied in layers over the outer skins of the stress-skin panels and roofing material such as shingles attached directly to the outer skins of the panels. A roof constructed in such a manner does not vent properly. Due to excessive heat buildup between the roofing materials and the stress-skin panels due to the insulation inside the panels, the stress-skin panels may deteriorate. Hence, the useful life of a roof constructed of stress-skin panels is limited.
One prefabricated roof panel which attempts to better ventilate a roof made from a plurality of panels is disclosed in U.S. Pat. No. 4,852,314. This patent discloses a generally planar deck spaced above a stress-skin panel by a plurality of spaced spacers between which air may flow up the roof and escape. The roofing panels disclosed in this patent have a substrate of rigid foam material sandwiched between two facer boards made of fiberglass. Conventional roofing materials such as asphalt-saturated felt and asphalt shingles are secured to the substantially planar deck portion of the panels. Although the roofing panels disclosed in this patent do provide ventilation, the panels are limited in size to the standard sizes of sheets of plywood or OSB. Additionally, these roofing panels must be attached to the rafters of a roof with nails or screws of a length greater than the depth of the panels. Therefore, the utility and longevity of such roofing panels are limited for the reasons described above.
In light of the aforementioned drawbacks of using stress-skin panels to construct the roof of a building, a need exists for a roofing panel which is structurally sounder than stress-skin panels and will not deteriorate or degrade over time due to seasonal temperature fluctuations. A need also exists for a roofing panel which may be made of a larger size than the size of one sheet of plywood or OSB so that the roof of a building may be constructed of a lesser number of panels than has heretofore been possible. Also a need exists for a roofing panel which does not require the use of fasteners or nails of a length greater than the depth of the panel in order to secure the panel to timber frame members such as rafters, purlins, plates or other timber frame members.
Therefore, it has been one objective of the present invention to provide an insulated roof panel less susceptible to degradation over time than stress-skin panels.
It has a further objective of the present invention to provide an insulated roof panel which does not require long screws or nails to pass through the panel in order to secure the insulated roof panel to the timber frame members of a building.
It has been a further objective of the present invention to provide an insulated roof panel which may span greater distances than stress-skin panels.
It has been a further objective of the present invention to provide an insulated roof panel which may be customized for particular applications.